Transmission/reception method and apparatus for uplink mimo retransmission in lte system

ABSTRACT

A transmission/reception method and apparatus for a mobile communication system supporting uplink MIMO is provided. In the transmission method, a User Equipment (UE) transmits two transport blocks according to a predetermined number of layers and respective precoding indices, an evolve Node B (eNB) transmits, when one of the transport blocks is lost, a negative acknowledgement for the lost transport block, and the UE sets a precoding index for the lost transport block to a predetermined value to retransmit the lost transport block while maintaining the number of layers.

PRIORITY

This application claims priority under 35 U.S.C. 119(a) to anapplication filed in the Korean Intellectual Property Office on Sep. 29,2010, and assigned Serial No. 10-2010-0094749, the content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a signaling method for use ofMultiple Input and Multiple Out (MIMO) in Uplink (UL) of Long TermEvolution (LTE) system and, more particularly, to a method fordetermining a precoding matrix without a separate control signal.

2. Description of the Related Art

Mobile communication systems have evolved into high-speed, high-qualitywireless packet data communication systems that provide data servicesand multimedia services that far exceed early voice-oriented services.Recently, various mobile communication standards have been developed tosupport services of the high-speed, high-quality wireless packet datacommunication systems. These standards include, for example, High SpeedDownlink Packet Access (HSDPA) and High Speed Uplink Packet Access(HSUPA), both defined in 3^(rd) Generation Partnership Project (3GPP),High Rate Packet Data (HRPD) defined in 3^(rd) Generation PartnershipProject-2 (3GPP2), and 802.16 defined by the Institute of Electrical andElectronics Engineers (IEEE).

The recent mobile communication systems use specific technologies, suchas an Adaptive Modulation and Coding (AMC) method and aChannel-Sensitive Scheduling (CSS) method, to improve the transmissionefficiency. Through the use of the AMC method, a transmitter can adjustan amount of transmission data according to a channel state.Specifically, when the channel state is bad, the transmitter reduces theamount of transmission data to adjust a reception error probability to adesired level. When the channel state is good, the transmitter increasesthe amount of transmission data to adjust the reception errorprobability to the desired level, thereby efficiently transmitting alarge volume of information. Through the use of a CSS-based resourcemanagement method, the transmitter selectively services a user having achannel state that is better than those of other users. This selectiveservicing provides an increase in the system capacity when compared to amethod of allocating a channel to one user and servicing the user withthe allocated channel. Such a capacity increase is referred to as‘multi-user diversity gain’. Thus, the AMC method and the CSS methodeach apply an appropriate modulation and coding scheme at themost-efficient time, which is determined based on partial channel stateinformation that is fed back from a receiver.

Research has been conducted in order to replace Code Division MultipleAccess (CDMA), the multiple access scheme used in the 2^(nd) and 3^(rd)generation mobile communication systems, with Orthogonal FrequencyDivision Multiple Access (OFDMA) in the next generation system. Thestandardization organizations, such as 3GPP, 3GPP2, and IEEE, have begunstandardizations of evolved systems employing OFDMA. The OFDMA schemeresults in a capacity increase when compared to the CDMA scheme. Onereason for the capacity increase in the OFDMA scheme is that the OFDMAscheme can perform scheduling in the frequency domain (frequency domainscheduling). While the transceiver acquires capacity gain according to atime-varying channel characteristic using the CSS method, thetransceiver can obtain a higher capacity gain through the use of afrequency-varying channel characteristic.

In LTE, Orthogonal Frequency Division Multiplexing (OFDM) has beenadopted for Downlink (DL) transmissions and Single Carrier FrequencyDivision Multiple Access (SC-FDMA) has been adopted for Uplink (UL)transmissions. Both transmission schemes are characterized by schedulingon frequency axis.

AMC and CSS are techniques that are capable of improving transmissionefficiency when the transmitter has enough information on the transmitchannel. In the LTE DL, the base station cannot estimate the DL channelstate using the UL receive channel in a Frequency Division Duplex (FDD)mode such that the UE reports the information on the DL channel.However, the DL channel report sent from the UE to the base station canbe omitted in a Time Division Duplex (TDD) mode in which the DL transmitchannel state is estimated through the UL receive channel. Meanwhile, inthe LTE UL, the UE transmits a Sounding Reference Signal (SRS) such thatthe base station estimates the UL channel using the received SRS.

In the LTE DL, the multiple antenna transmission technique, i.e., MIMO,is supported. The evolved Node B (eNB) of the LTE system can beimplemented with one, two or four transmit antennas, and thus, canachieve beamforming gain and spatial multiplex gain by adoptingprecoding with multiple transmit antennas.

Recently, UL MIMO for LTE has been discussed. In DL MIMO, the eNB, asthe transmitter, determines the transmission properties, such as, forexample, modulation and coding, MIMO, and precoding schemes. The eNB canconfigure and transmit a Physical Downlink Shared CHannel (PDSCH) andinform the UE of the transmission property applied to the PDSCH. In ULMIMO, the eNB, as the receiver, determines the transmission properties,such as, for example, modulation and coding, MIMO, and precodingschemes, according to the channel characteristics of each UE. The eNBnotifies the UE of the transmission properties through a PhysicalDownlink Control CHannel (PDCCH). The UE configures and transmits aPhysical Uplink Shared CHannel (PUSCH) by reflecting the transmissionproperties transmitted by the eNB. Specifically, the eNB always makes adecision on the AMC, CSS, and MIMO precoding, and the UE receives thePDSCH and transmits the PUSCH according to the decision made by the eNB.

If the eNB knows the exact channel state, it is possible to determinethe amount of data that is most appropriate for the channel state usingAMC. However, there is a difference between the channel state known tothe eNB and the actual channel state in the real environment due toestimation and feedback errors. Accordingly, it is impossible to avoiderrors in actual transmission/reception, even when AMC is applied.

In order to retransmit a signal that failed in its initial transmission,Hybrid Automatic ReQuest (HARQ) is adopted. In HARQ, the receiver sendsthe transmitter a negative acknowledgement (NACK) indicating a decodingfailure on the received data and an acknowledgement (ACK) indicatingsuccessful decoding on the received data, such that the transmitter canretransmit the lost data.

In a system using HARQ, the receiver combines the retransmitted signaland the previously received signal to improve the reception performance.The data signal that was previously received and failed in decoding issaved in a memory in consideration of retransmission. The HARQ processis configured such that the transmitter can transmit additional dataduring the time the ACK or NACK is transmitted by the receiver and thereceiver can determine one of the previously received signals to becombined with a retransmission signal based on the HARQ ProcessIDentifier (HARQ PID). The HARQ can be categorized into one ofsynchronous HARQ and asynchronous HARQ, depending on whether the HARQPID is notified by a control signal. In the synchronous HARQ, the HARQPID is provided in the functional relationship of the subframe sequencenumber carrying the PDCCH rather than through a control signal. Thesubframe is a unit of resource allocation on a time axis. In theasynchronous HARQ, the HARQ PID is provided by mans of the controlsignal. The LTE system employs the asynchronous HARQ for DL and thesynchronous HARQ for UL.

FIG. 1 is a diagram illustrating a conventional UL synchronous HARQprocess.

Referring to FIG. 1, the eNB sends an UL grant in PDCCH in an n^(th)subframe, as shown block 101. The HARQ PID is determined by the subframesequence n. For example, if the HARQ PID corresponding to the subframesequence number n is 0, the HARQ PID corresponding to the subframesequence number n+1 becomes 1. The PDCCH carrying the UL grant in then^(th) subframe includes a New Data Indicator (NDI). If the NDI istoggled from its previous value, the UL grant is an assignment of PUSCHfor a new data transmission. If the NDI is maintained, the UL grant isan assignment of PUSCH for retransmission of previously transmitteddata. Assuming that the UL grant of PDCCH 101 is transmitted with thetoggled NDI, the UE performs initial transmission of PUSCH carrying newdata in an (n+4)^(th) subframe, as shown in block 103. The UE can beaware of whether the PUSCH data transmitted in the (n+4)^(th) subframehas been successfully decoded through a Physical HARQ Indicator CHannel(PHICH) transmitted by the eNB in an (n+8)^(th) subframe, as shown inblock 105. If the PHICH carries a NACK, the UE performs PUSCHretransmission in an (n+12)^(th) subframe, as shown in block 107.

As described above, in the synchronous HARQ, the initial transmissionand retransmission of a Transport Block (TB) are performed inassociation with a sequence number of the subframe. Since the eNB and UEknow the TB that was initially transmitted in the (n+4)^(th) subframe isretransmitted in (n+12)^(th) subframe, it is possible to perform theHARQ process without the use of a separate HARQ PID. However, since thetransmission interval of the same TB is 8 subframes, the number of HARQprocesses that can be simultaneously active is limited to 8.

In the UL synchronous HARQ process of FIG. 1, the retransmission istriggered by the PHICH, which indicates only the HARQ ACK or NACK. If itis necessary for the eNB to change the PUSCH transmission property, suchas the transmission resource and modulation and coding scheme, forretransmission, it can be allowed to transmit in PDCCH indicating thischange. This HARQ scheme allowing for the change of the transmissionproperty is referred to as adaptive synchronous HARQ.

FIG. 2 is a diagram illustrating a conventional UL adaptive synchronousHARQ process.

Referring to FIG. 2, the eNB notifies the UE of a decoding failure ofthe PUSCH 103 in the (n+4)^(th) subframe by transmitting a NACK in PHICHin the (n+8)^(th) subframe, as shown in block 105. At this time, PDCCHis simultaneously transmitted with PHICH 105 in order to change thetransmission property, as shown in block 106. Since PDCCH decoding isattempted in every subframe, the UE can receive the PDCCH 106 for thetransmission property change. The UE performs PUSCH retransmission inthe (n+12)^(th) subframe based on the transmission property indicated bythe PDCCH, in block 108.

In the adaptive synchronous HARQ, even when the amount of DL controlinformation for retransmission increases to an amount that causesoverhead, the eNB can transmit PHICH with PDCCH for changing thetransmission property or without PDCCH for maintaining the transmissionproperty to minimize the amount of DL control information for the HARQoperation.

FIG. 3 is a flowchart illustrating operations of the eNB for thecovnetional UL adaptive synchronization HARQ procedure.

Referring to FIG. 3, the eNB performs UL scheduling to allocate aresource for PUSCH transmission to the UE with the UL grant, in step131. The eNB transmits PDCCH to grant an initial PUSCH transmission tothe scheduled UE, in step 133. The eNB receives and decodes PUSCH in thefourth subframe after the subframe where the PDCCH is transmitted, instep 135. The eNB determines whether the PUSCH decoding is successful,in step 137. If the PUSCH is decoded successfully, the eNB sends the UEan ACK, in step 139, and methodology returns to step 131 for newscheduling. If the PUSCH decoding fails in step 137, the eNB sends theUE a NACK, in step 141. According to the adaptive synchronous HARQoperation, the eNB determines whether it is necessary to change thetransmission property as compared to that of the initial transmission,in step 143. If it is not necessary to change the transmission property,the methodology returns to step 135 to receive and decode theretransmitted PUSCH. If it is necessary to change the transmissionproperty, the eNB transmits PDCCH to grant PUSCH retransmission havingthe new transmission property to the UE, in step 145. After transmittingthe NACK to request for retransmission, the methodology returns to step135 to receive and decode the retransmitted PUSCH.

FIG. 4 is a flowchart illustrating operations of the UE for theconventional UL adaptive HARQ procedure.

Referring to FIG. 4, the UE receives and decodes the PDCCH for UL grant,in step 151, and determines whether the PDCCH is decoded successfully,in step 153. If the PDCCH for UL grant is decoded successfully, the UEdetermines whether the NDI is toggled, in step 155. If NDI is toggled,it indicates that the UL grant is for an initial transmission of a newTB. Thus, the UE transmits a PUSCH carrying the new TB, in step 157. IfNDI is not toggled, this indicates that a previous TB having a same HARQPID was not decoded successfully, and the UE retransmits the PUSCHcarrying the previous TB with a transmission property according to anindication of the PDCCH, in step 159.

If the PDCCH for UL grant is not decoded successfully at step 153, theUE receives and decodes a PHICH, in step 161. Upon receipt of the PHICH,the UE determines whether the PHICH carries an ACK, in step 163. If thePHICH carries the ACK, the UE stops transmitting the PUSCH, in step 165.If the PHICH carries NACK, the UE transmits the PUSCH carrying theprevious TB with the transmission property indicated by a most recentlyreceived PDCCH, in step 167. However, the Redundancy Version (RV) of thePUSCH, which is retransmitted in PHICH, increases automatically withoutseparate instruction.

There are two main schemes for HARQ retransmission: Chase Combining (CB)and Incremental Redundancy (IR). CB is a method that combines an initialtransmission and its subsequent retransmission at the symbol level inthe receiver. IR is a method for combining an initial transmission andits retransmission having different RVs in the decoding process of thereceiver. In spite of its high complexity as compared to CB, the IR iswidely used for HARQ retransmission due to the additional decoding gain.Since the PDCCH for changing the RV in the synchronous HARQ is nottransmitted, the RV is determined implicitly. In the LTE system, a totalof 4 RVs are defined (RV=0, 1, 2, 3). In case of the synchronous HARQ,the RV is applied in order of {0, 1, 2, 3}, according to thetransmission order.

The Downlink Control Information (DCI) for UL grant for the PUSCHtransmission includes the following Information Elements (IE):

-   -   A flag for differentiating between DCI format 0 and DCI format        1A: Because DCI format 0 for UL grant and DCI format 1A for        compact DL assignment are always forced to be the same size in        LTE, there is a need to differentiate between format 0 and        format 1A.    -   Frequency hopping flag: This flag is an IE used to notify of the        use of frequency hopping for frequency diversity in PUSCH        transmission.    -   Resource assignment information: This IE is defined for        indicating the resource assigned for PUSCH transmission.    -   Modulation and Coding scheme: This is an IE that indicates the        modulation and coding scheme for use in PUSCH transmission. Some        codepoints of this IE are defined to indicate the RV for        retransmission.    -   NDI: This is an IE indicating whether the corresponding grant is        an initial transmission of a new TB or a retransmission. If its        value is toggled, it indicates a grant for a new TB transmission        and, otherwise, it indicates a grant for retransmission.    -   Transmit Power Control: This is an IE indicating the transmit        power for use in PUSCH transmission.    -   RS parameter Cyclic Shift Index (CSI): The RS for PUSCH        demodulation is defined with a Zadoff-Chu (ZC) sequence. The ZC        sequence has a characteristic in which the new ZA sequence is        acquired by changing the cyclic shift. The IE indicating the        cyclic shift of the RS for PUSCH demodulation is defined in the        UL grant for multiuser MIMO. By assigning the RSs having        different cyclic shift indices, the eNB can discriminate between        the signals of different users based on the orthogonality of the        RS.    -   Channel Quality Indicator (CQI) request: This is an IE for        requesting non-periodic CQI feedback on the PUSCH. This IE is 1        bit, and is set to 1 for transmission of non-periodic CQI, a        Precoding Matrix Indicator (PMI), and a Rank Indicator (RI)        along with data; and is set to 0 for data transmission only on        the PUSCH.

Unlike the case where both of the two TBs are successfully decoded ornot decoded, the eNB requesting UL MIMO transmission can define theprecoding operation of the UE without transmission of PDCCH. If one ofthe two TBs is successfully decoded, it is necessary to transmit thePDCCH indicating the precoding scheme of the UE. This characteristicdegrades the significant advantage of the synchronous HARQ. Thesynchronous HARQ can trigger retransmission only with PHICH, and withouttransmission of PDCCH. Unlike the PHICH carrying only the ACK/NACKinformation, PDCCH is designed to carry various control information suchthat the eNB consumes a relatively large amount of frequency resourcesand transmission power for PDCCH transmission. Specifically, one of theadvantages of the synchronous HARQ is to minimize the frequency resourceand transmission power consumption. Accordingly, the PDCCH transmissionfor retransmission grant causes an increase of resource consumption forthe control signal.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides a method for controlling UL HARQ only with PHICH, especiallywhen the retransmission of one TB is requested in the LTE systemsupporting UL MIMO.

In accordance with an aspect of the present invention, a transmissionmethod of a terminal supporting UL MIMO is provided. A plurality oftransport blocks are transmitted according to a predetermined number oflayers. A precoding index for a lost transport block is set to apredetermined value, when one of the plurality of transport blocks islost.

In accordance with another aspect of the present invention, a receptionmethod of a base station supporting UL MIMO is provided. Reception of aplurality of transport blocks is scheduled according to a predeterminednumber of layers. A negative acknowledgement is transmitted for a losttransport block, when one of the plurality of transport blocks is lost.A precoding index for reception of a retransmission of the losttransport block is set to a predetermined value.

In accordance with an additional aspect of the present invention, atransmitter of a terminal is provided that supports UL MIMO. Thetransmitter includes a Radio Frequency (RF) processor that transmits aplurality of transport blocks to a base station according to apredetermined number of layers. The transmitter also includes acontroller that sets a precoding index for a lost transport block to apredetermined value, when one of the plurality of transport blocks islost.

In accordance with still a further aspect of the present invention, areceiver of a base station is provided that supports UL MIMO. Thereceiver includes a controller that performs scheduling for reception ofa plurality of transport blocks according to a predetermined number oflayers. The receiver also includes an RF processor that transmitsnegative acknowledgement for a lost transport block, when one of theplurality of transport blocks is lost. The controller sets a precodingindex for reception of a retransmission of the lost transport block to apredetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a UL synchronous HARQ process;

FIG. 2 is a diagram illustrating a UL adaptive synchronous HARQ process;

FIG. 3 is a flowchart illustrating operations of the eNB for the ULadaptive synchronization HARQ procedure;

FIG. 4 is a flowchart illustrating operations of the UE for the ULadaptive HARQ procedure;

FIG. 5 is a block diagram illustrating a configuration of the UE forsupporting the UL MIMO, according to an embodiment of the presentinvention;

FIG. 6 is a block diagram illustrating a configuration of the eNB forsupporting the UL MIMO, according to an embodiment of the presentinvention;

FIG. 7 is a flowchart illustrating a procedure of the eNB for supportingUL MIMO, according to an embodiment of the present invention;

FIG. 8 is a flowchart illustrating a procedure of the UE for supportingnormal UL MIMO, according to an embodiment of the present invention;

FIG. 9 is a flowchart illustrating operations of the UE supporting ULMIMO, according to an embodiment of the present invention;

FIG. 10 is a flowchart illustrating operations of the eNB supporting ULMIMO, according to an embodiment of the present invention;

FIG. 11 is a flowchart illustrating operations of the UE supporting ULMIMO, according to an embodiment of the present invention; and

FIG. 12 is a flowchart illustrating operations of the eNB supporting ULMIMO, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention are described in detailwith reference to the accompanying drawings in detail. The same orsimilar components may be designated by the same or similar referencenumbers although they are illustrated in different drawings. Detaileddescriptions of constructions or processes known in the art may beomitted to avoid obscuring the subject matter of the present invention.

Although embodiments of the present invention are directed to the LTEsystem, the present invention is not limited thereto. For example, thepresent invention can be applied to any of the communication systemssupporting UL MIMO.

FIG. 5 is a block diagram illustrating a configuration of the UE forsupporting the UL MIMO, according to an embodiment of the presentinvention.

Referring to FIG. 5, the LTE system employs SC-FDMA in uplink.Typically, the Uplink Control Information (UCI), including UL ACK/NACKinformation for DL HARQ, CQI, PMI, and RI, is transmitted on a PhysicalUplink Control Channel (PUCCH), and the UL data is transmitted on thePUSCH. In the transmitting the UCI and UL data to maintain the singlecarrier property, the UCI is multiplexed on the PUSCH along with the ULdata rather than transmitted on the PUCCH. When the non-periodic CQI isrequested with UL grant, the non-periodic CQI, PMI, and RI istransmitted with data on PUSCH such that the UCI and the data aremultiplexed.

Function block 201 performs encoding and modulation to generate a datasignal, and function block 205 performs decoding and modulation togenerate a UCI signal. In the UE supporting UL MIMO, up to two codewords(hereinafter referred to as CW) are generated. Typically, the CWcorresponds to the TB, i.e., CW0 is equal to TB1 and CW1 is equal toTB2. When the swap function is activated, the relationship between CW0and TB1 can be changed such that CW0 corresponds to TB2 and CW1 to TB1.Although the swap function is defined in LTE DL MIMO, it may beunnecessary in UL MIMO.

The function block 201 applies different scrambling codes to generatethe CW according to the CW sequence. In the LTE system, the scramblingsequence can be a length-31 gold sequence c(n), as shown in Equation (1)below:

c(n)=(x,(n+N _(C))÷x ₂(n÷N _(C)))mod 2

x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2

x ₂(n÷31)=(x ₂(n+3)+(n+2)+x ₂(n+1)+x ₂(n))mod 2  (1)

In Equation (1),

-   -   Amod2 is a remainder obtained by dividing A by 2    -   N_(C)=1600    -   The initial value of x₁(n) is x₁(0)=1, and x₁(n)=0 for n=1, 2, .        . . , 30    -   The initial value of x₂(n) is expressed as Equation (2) below:

$\begin{matrix}{c_{init} = {{\sum\limits_{i = 0}^{30}\; {{x_{2}(i)} \cdot 2^{i}}} = {{n_{RNTI} \cdot 2^{14}} + {q \cdot 2^{13}} + {{\left\lfloor {n_{s}/2} \right\rfloor \cdot 2}{^\circ}} + N_{ID}^{cell}}}} & (2)\end{matrix}$

In Equation (2),

-   -   n_(RNTI) is a Radio Network Temporary Identifier (RNTI) in        association with PUSCH transmission    -   q is a CW sequence, q=0 for CW0 and q=1 for CW1    -   n_(s) is a sequence number of the first slot of a subframe        carrying PUSCH, and └n_(s)/2┘ is a sequence number of the        subframe carrying PUSCH    -   N_(ID) ^(cell) is an identifier of the serving cell

Among the signal lines denoted by reference number 203 in FIG. 5, thesolid line arrow means the generation of single CW, and the dotted linearrow means the generation of two CWs. The modulated data signalgenerated by the function block 201 and the modulated UCI signalgenerated by the function block 205 are multiplexed, interleaved, andmapped to a MIMO layer by function block 207. In LTE, the CW is mappedto the MIMO layer as shown in Table 1 below.

TABLE 1 # of layers (rank) # of CW CW-to-layer mapping 1 1 CW 0 → layer0: x⁽⁰⁾(i) = d⁽⁰⁾(i) 2 2 CW 0 → layer 0 & CW 1 → layer 1: x⁽⁰⁾(i) =d⁽⁰⁾(i) x⁽¹⁾(i) = d⁽¹⁾(i) 2 1 CW 0 → layers {0, 1}: x⁽⁰⁾(i) = d⁽⁰⁾(2i)x⁽¹⁾(i) = d⁽⁰⁾(2i + 1) only retransmission is allowed 3 2 CW 0 → layer 0& CW 1 → layers {1, 2}: x⁽⁰⁾(i) = d⁽⁰⁾(i) x⁽¹⁾(i) = d⁽¹⁾(2i) x⁽²⁾(i) =d⁽¹⁾(2i + 1) 4 2 CW 0 → layers {0, 1} & CW 1 → layers {2, 3}: x⁽⁰⁾(i) =d⁽⁰⁾(i) x⁽¹⁾(i) = d⁽¹⁾(2i) x⁽²⁾(i) = d⁽¹⁾(2i + 1)

In Table 1, d^((k)) denotes an i^(th) modulation symbol of CW k, andx^((l))(i) denotes an i^(th) symbol of an l^(th) layer. When a CW ismapped to two layers, the even-numbered modulation symbol is mapped tothe low layer, and the odd-numbered modulation symbol is mapped to thehigh layer. By mapping one CW to two layers, it is possible to transmitmore modulation symbols so as to increase the transmission data amountor decrease the coding rate, as compared to mapping one CW to one layer.

As shown in Table 1, for a rank-1 transmission, the number of CWs is 1for one layer and 2 for multiple layers. There is an exceptional casewhere one CW is transmitted in spite of rank-2 transmission and, in thiscase, only the retransmission is allowed.

The layer signals output by the function block 207 are precoded byfunction block 209. Precoding is per-layer beamforming that improvesreception quality on each layer. The precoding is determined inconsideration of the transmission channel property and, since thetransmission channel of UL MIMO is the UL channel, the eNB instructs theUE to use an appropriate precoder according to the UL channelmeasurement result. The UE performs precoding according to aninstruction from the eNB. The precoder is expressed as a matrix having anumber of rows that corresponds to a number of antennas, and a number ofcolumns that corresponds to a number of layers. Equation (3) shows theprecoding matrix.

$\begin{matrix}{y = {\begin{bmatrix}{y^{(0)}(i)} \\\vdots \\{y^{({N - 1})}(i)}\end{bmatrix} = {{Px} = {\begin{bmatrix}p_{11} & \cdots & p_{R\; 1} \\\vdots & \ddots & \vdots \\p_{N\; 1} & \cdots & p_{RN}\end{bmatrix}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({R - 1})}(i)}\end{bmatrix}}}}} & (3)\end{matrix}$

In Equation (3), x^((n))(i) denotes an i^(th) symbol to be transmittedby an nth transmit antenna. In an embodiment of the present invention,the transmit antenna is a logical antenna for signal transmission ratherthan a physical antenna. The mapping between the logical antennas andthe physical antennas can be defined diversely.

Table 2 shows precoding matrices for use in a situation using twotransmit antennas for LTE UL MIMO, and Table 3 shows precoding matricesfor use in a situation using four transmit antennas for LTE UL MIMO.

TABLE 2 Rank- 1 Indices 0~3 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}$ Indices 4~5 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\0\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}0 \\1\end{bmatrix}$ — — Rank- 1 Index 0 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}$ — — —

TABLE 3 Rank-1 Indices 0~3 $\frac{1}{2}\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\j \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\{- 1} \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\{- j} \\{- j}\end{bmatrix}$ Indices 4~7 $\frac{1}{2}\begin{bmatrix}1 \\j \\1 \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\j \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\{- 1} \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\{- j} \\{- 1}\end{bmatrix}$ Indices 8~11 $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\1 \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\j \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- 1} \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- j} \\j\end{bmatrix}$ Indices 12~15 $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\1 \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\j \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- 1} \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- j} \\1\end{bmatrix}$ Indices 15~19 $\frac{1}{2}\begin{bmatrix}1 \\0 \\1 \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\{- 1} \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\j \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\{- j} \\0\end{bmatrix}$ Indices 20~23 $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\{- j}\end{bmatrix}$ Rank-2 Indices 0~3 $\frac{1}{2}\begin{bmatrix}1 & 0 \\1 & 0 \\0 & 1 \\0 & {- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\1 & 0 \\0 & 1 \\0 & j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- j} & 0 \\0 & 1 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- j} & 0 \\0 & 1 \\0 & {- 1}\end{bmatrix}$ Indices 4~7 $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- 1} & 0 \\0 & 1 \\0 & {- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- 1} & 0 \\0 & 1 \\0 & j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\j & 0 \\0 & 1 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\j & 0 \\0 & 1 \\0 & {- 1}\end{bmatrix}$ Indices 8~11 $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\1 & 0 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\1 & 0 \\0 & {- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\{- 1} & 0 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\{- 1} & 0 \\0 & {- 1}\end{bmatrix}$ Indices 12~15 $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 1 \\1 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & {- 1} \\1 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 1 \\{- 1} & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & {- 1} \\{- 1} & 0\end{bmatrix}$ Rank-3 Indices 0~3 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\{- 1} & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\{- 1} & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ Indices 4~7 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\{- 1} & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\{- 1} & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ Indices 8~4 $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1 \\{- 1} & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0 \\{- 1} & 0 & 0\end{bmatrix}$ Rank-4 Index 0 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}$ — — —

A signal output by the function block 209 to be transmitted through thetransmit antenna. This signal is processed so as to be output in SC-FDMAsignal format appropriate for LTE UL transmission. Function block 211 ais the SC-FDMA signal convertor for the first transmit antenna, andfunction block 211 b is the SC-FDMA signal converter for the secondtransmit antenna. The SC-FDMA signal converter includes a DiscreteFourier Transform (DFT) precoder 221, a resource mapper 223, an InverseFast Fourier Transformer (IFFT) 225, and a Cyclic Prefix (CP) adder 227.

A Reference Signal (RS) is the signal provided for coherentdemodulation. The RS is generated per layer, and function blocks 231 aand 232 b are the RS generators. The function block 231 a is the RSgenerator for the first layer, and the function block 231 b is the RSgenerator for the last layer. The function block 209 performs precodingon the RSs of individual layers as applied to the PUSCH. Since the sameprecoding is applied to the RS and PUSCH, the eNB can receive the RS andestimates a channel for decoding per layer. Through the per-layer RSprecoding, the RSs are generated for transmission through respectivetransmit antennas.

In the LTE system, the UL RS is defined with a ZC sequence. The ZCsequence is characterized in that both the time domain signal and theFourier-transformed frequency domain signal are formed as a symbolhaving a predetermined size. The ZC sequences acquired by applyingdifferent cyclic shifts (CS) to a basic ZC sequence are orthogonal witheach other. In the LTE system, 12 CSs are supported for UL RS. Multipleusers can share the frequency-time resource for PUSCH transmission, andthe UL multiuser MIMO is implemented by assigning the CSs derived fromdifferent ZC sequences to the respective users. The PDCCH for grantingPUSCH transmission includes a 3-bit Cyclic Shift Index (CSI) fornotifying the ZC sequence of the CS for UL RS. In order to reinforce theorthogonality of the RS, a length-2 Walsh code is applied to the RStransmitted in the two slots of the subframe carrying PUSCH on the timeaxis. This Walsh code is referred to as an Orthogonal Cover Code (OCC),and the CSI indicates one of [+1, +1] and [+1,−1] as the OCC.

For UL single user MIMO, multiple layers are configured for PUSCHtransmission. Each layer uses a unique RS having orthogonality, and theCSI of PDCCH notifies of the CS and OCC for the first layer RS. The CSand OCC of the second or next layer RS is determined by the layer numberby referencing the CS and OCC of the first layer RS. Specifically, if kis the layer number and if the CS and OCC of the k^(th) layer RS areCS_(k) and OCC_(k), the CSI of PDCCH indicates only the CS₁ and OCC₁,such that the CS_(k) and OCC_(k) are determined in functions of CS₁ andk and OCC₁ and k. CS_(k) and OCC_(k) are described in detail withreference to Equation (4) below.

CS _(k)+(CS ₁+Δ_(k))mod 12

OCC _(k)=(OCC ₁+δ_(k))mod 2  (4)

In Equation (4), A, denotes a CS offset value for determining the k_(th)layer CS, and δ_(k) denotes an OCC offset value for determining thek_(th) layer OCC.

The Δ_(k) and δ_(k) for determining S_(k) and OCC_(k) are shown in Table4.

TABLE 4 Offset k 1 2 3 4 Δ_(k) 0 6 3 9 δ_(k) 0 0 1 1

The SC-FDMA signals of PUSCH to be transmitted by the respectivetransmit antennas are multiplexed with the corresponding RSs by functionblocks 213 a and 213 b in FIG. 5. The function block 213 a is amultiplexer for multiplexing PUSCH and RS to be transmitted by the firsttransmit antenna, and function block 213 b is a multiplexer formultiplexing PUSCH and RS to be transmitted by the second transmitantenna. In order to maintain the single carrier property, the RS andPUSCH are multiplexed on the time domain (time division multiplexing) soas to be transmitted in different SC-FDMA symbols.

The baseband signals to be transmitted by the transmit antennas of theUE are converted to RF signals by RF processors 215 a and 215 b and thentransmitted through transmit antennas 217 a and 217 b. The RF processors215 a and 215 b process the signals to be transmitted through the firstand last transmit antennas. 217 a and 217 b represent the first and lasttransmit antennas.

The reception part of the UE includes a receive combiner 251, a PDCCHreceiver 253, and a PHICH receiver 255. The receive combiner 251combines the signals received by multiple receive antennas. The combinedsignal is delivered to the PDCCH receiver 253 and the PHICH receiver255. The PDCCH receiver 253 receives the control signal when the eNB hastransmitted the DCI signal for adaptive HARQ, and the PHICH receiver 255receives the control signal when the eNB has transmitted ACK/NACK signalon PHICH. The DCI signal of PDCCH and ACK/NACK signal of PHICH aredelivered to a controller 241.

When two TBs are transmitted on the UL PUSCHs, the ACK/NACK stateinformation per TB is transmitted to the eNB on PHICH. The resource fortransmitting DL ACK/NACK information for UL PUSCH transmission isexpressed as (n_(PHICH) ^(group),n_(PHICH) ^(seq)). Here, n_(PHICH)^(group) denotes the PHICH group number, and n_(PHICH) ^(seq) denotesthe PHICH sequence number in the corresponding PHICH group. PHICH is thechannel for transmitting one of the ACK and NACK using Binary PhaseShift Keying (BPSK) modulation scheme, and 2N_(SF) ^(PHICH) ACK/NACKinformation are multiplexed into one PHICH group using a unique PHICHsequence. Before UL single user MIMO is introduced, only one PHICH isallocated per user but, with the introduction of the UL single userMIMO, it becomes necessary to assign two PHICHs to the user which hastransmitted two TBs, as shown in Equation (5).

n _(PHICH) ^(group)=(I _(PRB) _(—) _(RA) +n _(DMRS))mod N _(PHICH)^(group) +I _(PHICH) N _(PHICH) ^(group)

n _(PHICH) ^(seq)=(└I _(PRB) _(—) _(RA) /N _(PHICH) ^(group) ┘+n_(DMRS))mod 2N _(SF) ^(PHICH)  (5)

In Equation (5), n_(DMRS) denotes the value determined by CSI of UL RS,CSI is indicated explicitly in PDCCH carrying the information on the ULPUSCH. N_(SF) ^(PHICH) denotes the spreading factor for use inmodulation of PHICH, and a PHICH group includes 2N_(SF) ^(PHICH) PHICHs.N_(PHICH) ^(group) denotes the total number of PHICH groups and isnotified by the eNB in advance. I_(PHICH) is set to 1 when a specificcondition for increasing the size of the PHICH group is fulfilled, and 0in all other cases. I_(PRB) _(—) _(RA) is a value determined by theResource Block (RB) on the frequency axis, which is used for PUSCHtransmission and indicated explicitly in PUSCH carrying the informationon the UL PUSCH. The PHICH resource for transmitting ACK/NACKinformation on the first TB is determined by I_(PRB) _(—) _(RA)=I_(PRB)_(—) _(RA) ^(lowest) ^(—) ^(index). The PHICH resource for transmittingACK/NACK information on the second TB is determined by I_(PRB) _(—)_(RA)=I_(PRB) _(—RA) ^(lowest) ^(—) ^(index). Here, I_(PRB) _(—RA)^(lowest) ^(—) ^(index) is the RB index having the least value among theRBs used for PUSCH transmission.

The controller 241 controls the PHICH receiver 255 to determine thePHICH resource for detecting ACK/NACK signal per TB and controls otherfunction blocks to perform UL HARQ operations using the receivedACK/NACK signal.

The controller 241 controls the overall operations of the UE so as todetermine a frequency resource for PUSCH transmission, a modulation andcoding scheme for the data and UCI transmitted on PUSCH, a resourceamount to be allocated for UCI in the PUSCH resource, a rank of MIMOtransmission, a precoding scheme, and a parameter for generating RS pertransmit antenna and control function blocks of the resource arrangement223, data and UCI encoding and modulation 201 and 205, data and UCImultiplex and interleaving and CW-layer mapping 207, precoding 209, andRS generation 231. The controller 241 controls the receipt of PDCCH andPHICH.

FIG. 6 is a block diagram illustrating a configuration of the eNB forsupporting the UL MIMO, according to an embodiment of the presentinvention.

Referring to FIG. 6, 301 a denotes a first receive antenna of the eNB,and 301 b denotes a last receive antenna of the eNB. The signalsreceived by a plurality of receive antennas of the eNB are converted tobaseband signals by RF processors 303 a to 303 b. 303 a denotes a firstRF processor for processing the signal received by the first receiveantenna 301 a, and 303 b denotes a last RF processor for processing thesignal received by the last receive antenna 301 b. The baseband signalsconverted from the signals received by the receive antennas arerecovered into modulation symbol streams by SC-FDMA receivers 305 a to305 b. 305 a denotes a first SC-FDMA receiver for processing the signalreceived by the first receive antenna 301 a, and 305 b denotes a lastSC-FDMA receiver for processing the signal received by the last receiveantenna 301 b.

Each of the SC-FDMA receivers 305 a to 305 b includes a CP remover 331,a Fast Fourier Transform (FFT) 333, a resource demapper 335, and an IDFT337, and performs an operation that is inverse that of the SC-FDMAsignal converter 211 of FIG. 5.

The signal output by an SC-FDMA receiver is the PUSCH and RS transmittedby a specific UE. Since the PUSCH and RS are multiplexed in time domain,each of demultiplexers 307 a to 307 b separates the PUSCH and RS ofcorresponding UE. 307 a denotes a first demultiplexer for processing thesignal received by the first receive antenna 301 a, and 307 b denotes alast demultiplexer for processing the signal received by the lastreceive antenna 301 b. The RSs demultiplexed from the receive signalsare transferred to a channel estimator 311, and the PUSCH signalsdemultiplexed from the receive signals are transferred to a MIMO receivefilter 315.

The channel estimator 311 estimates an uplink channel using the receivedRSs and transfers the estimation results to a controller 313 such thatthe controller 313 calculates an appropriate receive filter coefficient.The receive filter coefficient is transferred to a MIMO receive filter315. The MIMO receive filter performs an operation that is inverse thatof the precoder 209 of FIG. 5 so as to separate the per-layer PUSCHsignals. The MIMO receive filter can be embodied as a Minimum MeanSquare Error (MMSE) receive filter.

The per-layer receive signals are converted to the CW modulation signalstreams and UCI modulation signal streams. Function block 317 performssteps that are inverse those of the function block 207 of FIG. 5 so asto include combining the layer signals per CW, interleaving the per-CWsignals, and demultiplexing data and UCI. Since the process is performedbased on the control information received from the UE in advance, thecontroller 313 having the control information controls the operations inthe process.

Per-CW modulation signals 319 output by the function block 317 aretransferred to a data demodulation and decoding block 321 and the UCImodulation signal is transferred to the UCI demodulation and decodingblock 323. The base station receives the data successfully and performsUL and DL scheduling and AMC based on the UCI information.

The DCI of the grant for PUSCH transmission in UL MIMO further includesthe following IEs.

-   -   PMI: An IE that notifies of a precoding scheme using UL MIMO        transmission    -   Modulation and coding scheme for second TB: up to 2 TBs can be        transmitted in UL MIMO. Accordingly, it is necessary to define        the IE notifying of the modulation and coding scheme for the        second TB.    -   NDI for second TB: NDI can be defined per TB or for both the two        TBs in UL MIMO. Although embodiments of the present invention        are directed to the case where the TB is defined per NDI,        additional embodiments of the present invention can be applied        to the case where one NDI is defined for two TBs.

The eNB transmits PHICH and PDCCH for supporting a UL HARQ operation. APHICH transmitter 351 transmits an ACK/NACK signal, and a PUSCHtransmitter 353 transmits a DCI signal including a PUSCH grant. Afterbeing precoded by a transmit precoder 355, the PDCCH and PHICH signalsare transferred to a plurality of transmit antennas. The controller 313determines the transmission signal and resource, and controls the PDCCHtransmitter 353 and PHICH transmitter 351.

FIG. 7 is a flowchart illustrating a procedure of the eNB for supportingUL MIMO, according to an embodiment of the present invention. Theprocedure of FIG. 7 shows the operations of the controller 313 of FIG. 6that are related to the UL MIMO. The PUSCH grant for transmitting one TBis similar to the procedure of FIG. 3.

Referring to FIG. 7, the eNB performs UL scheduling to determine theresource for PUSCH grant to a certain UE, in step 131. The eNB transmitsPDCCH carrying the PUSCH grant information to the scheduled UE, in step401. Assuming the UL MIMO transmission, the rank-2 or higher ranks isinformed to the UE. Specifically, it is assumed that two TBtransmissions are granted. In the fourth subframe after the subframe inwhich the PDCCH has been transmitted, the eNB performs demodulation anddecoding on PUSCH, in step 135. The eNB determines whether the PUSCH isdecoded successfully, in step 403. Since the two TBs are transmitted,the determination result, can be one of the following cases.

-   -   Case 1: TB1 and TB2 are successfully decoded such that the eNB        transmit PHICH carrying ACK/NACK, in step 405, and the        methodology proceeds to step 131.    -   Case 2: TB1 is successfully decoded but TB2 isn't such that the        eNB transmits PHICH carrying ACK/NACK, in step 407, and the        methodology proceeds to step 415.    -   Case 3: TB2 is successfully decoded but TB2 isn't such that the        eNB transmits PHICH carrying ACK/NACK, in step 409, and the        methodology proceeds to step 415.    -   Case 4: Decoding fails for both TB1 and TB2 such that the eNB        transmits PHICH carrying ACK/NACK, in step 413, and the        methodology proceeds to step 415.

In step 415, the eNB determines whether to change the transmissionproperty as compared to the transmission property of the initialtransmission of step 401. If it is determined to change the transmissionproperty, the methodology proceeds to step 411 and, otherwise, the eNBreceives the PUSCH under the assumption of retransmission of the UEwithout changing the transmission property of the initial transmissionand the methodology proceeds to step 135.

In step 411, the eNB transmits the PDCCH notifying the UE of thetransmission property to be used in retransmission. Under the assumptionthat that the PUSCH is transmitted using the transmission property whichis newly notified by the eNB, the UE receives and decodes the PUSCH andthe methodology proceeds to step 135.

Although it is possible to request the PUSCH retransmission bytransmitting only the PHICH without PDCCH transmission in the first andfourth cases, it is necessary to transmit PDCCH informing of thetransmission property for PUSCH retransmission in the second and thirdcases in which one of the two TBs is decoded successfully.

As summarized in Table 1, a number of TBs to be transmitted isdetermined depending on the value of the rank. If one of the two TBstransmitted in initial transmission is successfully decoded, there is noneed to transmit the successfully decoded TB such that one TB is sent inthe retransmission. As the number of TBs decreases, the value of therank also decreases in the retransmission as compared to the initialtransmission.

As shown in Tables 2 and 3, the precoder is defined differentlydepending on the rank. Accordingly, the precoder used in the initialtransmission cannot be used for retransmission. In the PUSCHtransmission based on the information of PDCCH, the scrambling sequenceper TB and CS and OCC to be applied to the UL RS and the PHICH resourceper TB are explicit. However, if the number of TBs decreases in PUSCHtransmission based on the PHICH information, the scrambling sequence perTB and CS and OCC to be applied to the UL RS and the PHICH resource forchecking ACK/NACK response of the eNB become unclear.

FIG. 8 is a flowchart illustrating a procedure of the UE for supportingUL MIMO, according to an embodiment of the present invention.

Referring to FIG. 8, the UE receives PDCCH for UL grant and attemptsdecoding the PDCCH, in step 151. The UE determines whether decoding issuccessful, in step 153. If the PDCCH for UL grant is decodedsuccessfully, the UE determines whether at least one NDI is toggled, instep 431. Assuming the UL MIMO transmission, the initial grant has theinformation on the two TBs. Assuming that NDI is defined per TB, if bothof the two NDIs are not toggled, this means that the UL grant is arequest for retransmission, and thus, the UE retransmits the PUSCH witha new transmission property including a PMI, in step 435. If at leastone of the NDIs is toggled, the methodology proceeds to step 433 wherethe TB corresponding to the toggled NDI is of an initial transmissionand the TB corresponding to non-toggled NDI is of a retransmission.Regardless of whether the TB is set in initial transmission orretransmission, the transmission property including PMI follows thevalue indicated in the corresponding PDCCH. Although only one NDI isdefined regardless of the number of TBs, if the NDI is not toggled, themethodology proceeds to step 433 for initial transmission of a new TBand, otherwise if the NDI is toggled, the methodology proceeds to step435 for retransmission. In terms of precoding, if PDCCH is received, theUE transmits the precoded PUSCH reflecting the PMI indicated by thePDCCH regardless of the retransmission of TB.

If no PDCCH is received, the UE receives PHICH and attempts decoding thePHICH, in step 441. In step 443, it is determined if an ACK is receivedfrom the PHICH. Assuming that the PHICH has the ACK/NACK informationrelated to the TBs, three cases are possible. Case 1 is that ACKs arereceived for both of the two TBs such that the UE transmits no PUSCH, instep 445. Case 2 is that an ACK is received for one TB and a NACK forthe other TB. In this case, the number of TBs to be retransmitteddecreases such that it is inevitable to change the value of the rank.However, since the eNB has not notified of PMI, it is unclear whichprecoding scheme is applied for PUSCH transmission. Accordingly, it isimpossible to define the PUSCH transmission operation of thecorresponding UE in step 447. Case 3 is that NACKs are received for bothof the two TBs such that it is necessary to send the two TBs inretransmission. In this case, there is no change in rank and nonotification of PMI by eNB, the UE retransmits the PUSCH using thetransmission property including PMI indicated in the most recentlyreceived UL grant. However, the RV should be changed for retransmissionaccording to the rule of the IR-based synchronous HARQ.

Embodiments of the present invention provide the following for definingoperations of the eNB and UE in a situation where the UL HARQretransmission is requested only with PHICH in the LTE system supportingUL MIMO.

-   -   Scrambling sequence of the TB in retransmission    -   Parameter of UL RS for retransmission, CS and OCC    -   PHICH resource corresponding to the TB in retransmission

Specifically, the UE supports the UL MIMO according to an embodiment ofthe present invention. The UE transmits a plurality of TBs to the eNB.The UE transmits the TBs using the UL RS parameters corresponding to therespective TBs. When the eNB does not receive one of the TBs, the UEconfigures the CW of the lost TB. If the PHICHs corresponding to the TBsare received from the eNB, the UE determines whether each TB is receivedsuccessfully based on the PHICHs. The UE also determines the propertyparameter corresponding to the configured CW. The UE also retransmitsthe lost TB to the eNB according to the determined property parameter.

The UE determines the property parameter independently. Specifically,the UE determines the scrambling sequence corresponding to theconfigured CW. The UE selects one of the previously used UL RSparameters for retransmission of the mission TB. The UE can determinethe offset value for CS and the offset value for OCC according thedetermined UL RS parameter. The UE also determines the PHICH resourcefor observing whether the retransmitted TB is received successfully.

The eNB also supports the UL MIMO according to embodiments of thepresent invention. The eNB receives a plurality of TBs and sends the UEa response indicating whether the individual TBs are receivedsuccessfully. The eNB transmits the response per TB on the PHICH. If oneof the TBs is lost, the eNB configures the CW of the lost TB anddetermines the property parameter corresponding to the configured CW.The eNB receives the lost TB that is retransmitted according to thedetermined property parameter, and sends the response indicating whetherthe retransmission of the lost TB is successful. The eNB transmits theresponse through the PHICH.

The eNB determines the property parameter independently. The eNB doesnot provide the UE with the property parameter. Specifically, the eNBdetermines the scrambling sequence corresponding to the configured CW.The eNB also selects one of the previously used UL RS parameters thatmatches the lost TB. The eNB can determine the offset values of the CSand OCC according to the determined UL RS parameter. The eNB alsodetermines the PHICH resource for transmitting information on whetherthe retransmission of the lost TB is successful.

The transceivers of the UE and eNB are configured as shown in FIGS. 5and 6, respectively. According to an embodiment of the presentinvention, the configurations of the controller 241 of FIG. 5 and thecontroller 313 of FIG. 6 should be modified.

The controller 241 of the UE is provided with a judgment unit, aconfiguration unit, and a determination unit. The controller 241transmits a plurality TBs to the eNB by the RF processors 215 a-215 band then detects the receipt of the PHICH from the eNB by the PHICHreceiver 255. The judgment unit judges whether each TB is successfullyreceived. If one of the TBs is lost, the judgment unit notifies theconfiguration unit of the lost TB. The configuration unit reconfiguresthe codeword of the lost TB. The determination unit determines theproperty parameter corresponding to the configured codeword. In thismanner, the controller 241 retransmits the lost TB to the eNB accordingto the determined property parameter.

The controller 241 transmits two TBs to the eNB. The controller 241transmits the TBs according to the property parameters received from theeNB. The property parameters include the number of layers and precodingindices of the individual TBs. If it is detected that one of the two TBsare not received by the eNB, the controller 241 sets the precoding indexfor retransmitting the lost TB to a predetermined value. The controller241 can set the precoding index to 0. The controller 241 maintains thenumber of layers. The controller 241 also retransmits the lost TB usingthe corresponding precoding index. Otherwise, if it is determined thatboth the two TBs are not received by the eNB, the controller 241maintains the property parameters and retransmits the lost TBs using theproperty parameters.

The controller 313 of the eNB is provided with a configuration unit anda determination unit. Specifically, the controller 313 receives aplurality of TBs from the UE by the RF processors 303 a-303 b and sendsthe eNB the PHICH indicating whether each of the TBs is receivedsuccessfully. If one of the TBs is not received, the configuration unitconfigures the CW of the lost TB. The determination unit determines theproperty parameter corresponding to the configured CW. In this manner,the controller 313 controls reception of the lost TB from the UE by theRF processors 303 a-303 b and sends the UE the PHICH indication,indicating whether the retransmission of the lost TB is successful.

The controller 313 performs scheduling to allocate resources forreceiving the TBs transmitted by the UE. The controller 313 determinesthe property parameters and sends the property parameters to the UE.Afterward, the controller 313 attempts to receive the lost TBs accordingto the property parameters. The property parameters include the numberof layers and precoding indices for the TBs. If one of the two TBs isnot received, the controller 313 sends a response signal for the lostTB. The controller 313 also sets the precoding index of the lost TB to apredetermined value. The controller 313 can set the precoding index to0. The controller 313 maintains the number of layers. Afterward, thecontroller 131 receives the retransmitted TB according to thecorresponding precoding index. If both of the two TBs are not received,the controller 313 maintains the property parameters and receives theTBs according to the property parameters.

In an embodiment of the present invention, when the PHICH indicatesretransmission of one of the two TBs of the initial transmission, theretransmitted TB is regarded as CW0 regardless of the sequence number ofthe retransmitted TB.

Table 5 summarizes scrambling, UL RS, and PHICH determined according tothis embodiment of the present invention.

TABLE 5 (NACK, (ACK, Item NACK) (NACK, ACK) NACK) (ACK, ACK) ScramblingUse previous Use q = 0 in equation (2) Retransmission UL RS transmissionUse k = 1 or k = 1, 2 in is not necessary rule equation (4)* PHICH UseI_(PRB) _(—) _(RA) = I_(PRB) _(—) _(RA) ^(lowest) ^(—) ^(index) inequation (5)

k=1 is used for a TB in a single layer retransmission, and k=1 is usedfor the TB on the first layer and k=2 is used for the TB on the secondlayer in a dual layer retransmission.

According to this embodiment of the present invention, the CW sequenceis reconfigured regardless of the CW corresponding to the TB in theprevious transmission. The scrambling, UL RS, and PHICH are determinedaccording to the reconfigured CW sequence.

FIG. 9 is a flowchart illustrating operations of the UE supporting ULMIMO, according to an embodiment of the present invention.

Referring to FIG. 9, the UE is in a state in which no PDCCH, for PUSCHretransmission caused by the reception failure of the two TBs in theprevious transmission, is received in step 501. The UE receives anddecodes the PHICHs, in step 503. Specifically, the UE is about totransmit the PUSCH based on the information carried in PHICHs. The UEdetermines whether the PHICH includes a ACK/NACK, in step 505. When ACKsare received for the two TBs (case 1), the UE stops the PUSCHretransmission, in step 507. When NACKs are received for the two TBs(case 3), the UE retransmits the two TBs in the same transmission rule,in step 509, and monitors the same PHICH(s) to detect the receipt of theACK/NACK for the retransmitted TBs, in step 511. When an ACK is receivedfor one of the two TBs and a NACK is received for the other of the twoTBs (case 2), the UE regards the TB as retransmitted as CW0, retransmitsthe corresponding TB using the scrambling sequence acquired by applyingq=0 to Equation (2) and the UL RS for the first layer or the first andsecond layers, which is obtained using the first layer UL RS parameterindicated in the most recently received PDCCH, in step 521. The UEmonitors to detect receipt of the PHICH on the PHICH resource determinedby applying I_(PRB) _(—) _(RA)=I_(PRB) _(—RA) ^(index) to Equation (5)to receive ACK/NACK for the retransmitted TB, in step 523.

When generating the UL RS for the first layer or the first and secondlayers, in step 521, the UE generates the UL RS (k=1) for the firstlayer when the retransmitted TB has occupied one layer in the previousPUSCH transmission, and generates the UL RS (k=1, 2) for the first andsecond layers when the retransmitted TB has occupied two layers in theprevious PUSCH transmission.

FIG. 10 is a flowchart illustrating operations of the eNB supporting ULMIMO, according to an embodiment of the present invention.

Referring to FIG. 10, when one of the two TBs received in the previoustransmission of the UE is decoded successfully but the other has failedto decode, the eNB sends (ACK, NACK) or (NACK, ACK) on the PHICH with noPDCCH, in step 601. The eNB regards the TB as retransmitted as CW0, andreceives the corresponding TB using the scrambling sequence obtained byapplying q=0 to Equation (2) and the UL RS for the first layer or thefirst and second layers, in step 603. The eNB sends the ACK/NACK for theretransmitted TB on the PHICH resource determined by applying I_(PRB)_(—) _(RA)=I_(PRB) _(—RA) ^(lowest) ^(—) ^(index) to Equation (5), instep 605.

In the embodiment of the present invention described above, scrambling,the UL RS, and the PHICH are determined according to the index number ofthe TB to be retransmitted as shown in Table 6.

TABLE 6 Item (NACK, NACK) (NACK, ACK) (ACK, NACK) (ACK, ACK) ScramblingUse previous Use q = 0 in Apply q = 1 to Retransmission transmissionequation (2) equation (2) is not UL RS rule Reuse UL RS Reuse UL RSnecessary parameter used parameter used for TB1 in for TB2 in previousprevious transmission transmission PHICH Apply Apply I_(PRB) _(—) _(RA)= I_(PRB) _(—) _(RA) = I_(PRB) _(—) _(RA) ^(lowest) ^(—) ^(index)I_(PRB) _(—) _(RA) ^(lowest) ^(—) ^(index) + 1 to equation (5) toequation (5)

According to another embodiment of the present invention, the TB to beretransmitted maintains the CW sequence assigned in the previoustransmission. The second embodiment is advantageous in that the eNB canreceive the TB retransmitted in response to the normally received NACKeven when it has failed to receive one of the ACK/NACK signalstransmitted by the UE. Assuming that the UE mis-interprets the (ACK,NACK) signal transmitted by the eNB for retransmission of TB2 as (NACK,NACK) signal, as a consequence, the UE retransmits both the TB1 and TB2.According to the embodiment of the present invention described above,the eNB attempts to receive TB2 corresponding to CW0 but the UEretransmits TB1 corresponding to CW0 and TB2 corresponding to CW1. Sincethe scrambling sequence and the UL RS for the TBs are interpreteddifferently by the eNB and the UE, the eNB cannot receive any of theretransmitted TBs in that the operation is not defined in considerationof such a situation. In this embodiment of the present invention, theeNB attempts to receive the TB2 corresponding to CW1, while the UEtransmits both the TB1 corresponding to CW0 and the TB2 corresponding toCW1. Although it is impossible to receive the TB1 corresponding to CW0,the eNB can receive the TB2 corresponding to CW1 normally. According tothis embodiment of the present invention, the eNB can receive theretransmitted TB2 in an erroneous situation without an additionalprocess for the erroneous situation.

In order to support this embodiment of the present invention, it isnecessary to define CW-layer mapping for retransmission of only the CW1as shown below in Table 7.

TABLE 7 # of layers # Mapping (rank) of CWs CW-to-layer mapping 1 1 1 CW0 → layer 0: x⁽⁰⁾(i) = d⁽⁰⁾(i) 2 1 1 CW 1 → layer 0: x⁽⁰⁾(i) = d⁽¹⁾(i) 32 2 CW 0 → layers 0 & CW 1 → layer 1: x⁽⁰⁾(i) = d⁽⁰⁾(i) x⁽¹⁾(i) =d⁽¹⁾(i) 4 2 1 CW 0 → layers {0, 1}: x⁽⁰⁾(i) = d⁽⁰⁾(2i) x⁽¹⁾(i) =d⁽⁰⁾(2i + 1) only retransmission is allowed 5 2 1 CW 1 → layers {0, 1}:x⁽⁰⁾(i) = d⁽¹⁾(2i) x⁽¹⁾(i) = d⁽¹⁾(2i + 1) only retransmission is allowed6 3 2 CW 0 → layer 0 & CW 1 → layers {1, 2}: x⁽⁰⁾(i) = d⁽⁰⁾(i) x⁽¹⁾(i) =d⁽¹⁾(2i) x⁽²⁾(i) = d⁽¹⁾(2i + 1) 7 4 2 CW 0 → layers {0, 1} & CW 1 →layers {2, 3}: x⁽⁰⁾(i) = d⁽⁰⁾(i) x⁽¹⁾(i) = d⁽¹⁾(2i) x⁽²⁾(i) = d⁽¹⁾(2i +1)

In comparison with Table 1, Table 7 further includes mapping 2 andmapping 5.

FIG. 11 is a flowchart illustrating operations of the UE supporting ULMIMO, according to an embodiment of the present invention.

Referring to FIG. 11, the UE is in a state in which no PDCCH is receivedfor the PUSCH retransmission, after sending two TBs in the previoustransmission, in step 501. The UE receives PHICHs, in step 503.Specifically, the UE is about to retransmit the PUSCH based on theinformation of the PHICH. Upon receipt of the PHICHs, the UE checks theACK/NACK of the PHICH, in step 705. If the PHICH carries ACKs for bothrespective TBs (case 1), the UE stops retransmission of PUSCH, in step507. If the PHICH carriers NACKs for both respective TBs (case 3), theUE retransmits the two TBs using the previous transmission rule, in step509, and monitors the same PHICHs to detect the receipt of ACK/NACK forthe retransmitted TBs, in step 511.

If the PHICH carries a NACK and an ACK for TB1 and TB2, respectively,such that it is necessary to retransmit only the TB1 (case 2), the UEregards the TB to be retransmitted as CW0, and the corresponding TB istransmitted using the scrambling sequence obtained by applying q=0 toEquation (2) and the first layer UL RS or the first and second layers ULRS obtained using the UL RS parameter of the first layer, which isindicated in the most recently received PDCCH, in step 721. The UEmonitors the PHICH associated with I_(PRB) _(—) _(RA)=I_(PRB) _(—) _(RA)^(lowest) ^(—) ^(index) applied to Equation (5) for receiving ACK/NACKfor the retransmitted TB, in step 723.

In step 721, the UE reuses the same first layer UL RS when the UL RS(k=1) has been used for TB1 in the previous PUSCH transmission, and thesame first and second layers UL RS when the UL RS (k=1, 2) has been usedfor TB1 in the previous PUSCH transmission.

If the PHICH carries an ACK and a NACK for TB1 and TB2, respectively,such that it is necessary to retransmit only the TB2 (case 3), the UEregards the TB to be transmitted as CW1, and the corresponding TB isretransmitted using the scrambling sequence obtained by applying q=1 toEquation (2) and the second layer UL RS or the second and third layersUL RS or the third and fourth layers UL RS obtained by applying the ULRS parameter of the first layer, which is indicated in the most recentlyreceived PDCCH, in step 731. In order to receive the ACK/NACK for theretransmitted TB, the UE monitors PHICH associated with I_(PRB) _(—RA)=I_(PRB) _(—) _(RA) ^(lowest) ^(—) ^(index)+1 applied to Equation (5),in step 733. In step 731, the UE reuses the same UL RS when the secondlayer UL RS (k=2) has been used for TB 2 in the previous PUSCHtransmission, the same UL RS when the second and third layers UL RS(k=2, 3) has been used for TB2 in the previous PUSCH transmission, andthe same UL RS when third and fourth layers UL RS (k=3, 4) has been usedfor TB2 in the previous PUSCH transmission.

FIG. 12 is a flowchart illustrating operations of the eNB supporting ULMIMO, according to an embodiment of the present invention.

Referring to FIG. 12, the eNB is in a state in which one of the two TBsreceived in the previous transmission of the UE is decoded successfully,but the other has failed in decoding, such that the eNB transmits an(ACK, NACK) signal or an (NACK, ACK) signal to the UE on the PHICH withno PDCCH for granting PUSCH retransmission, in step 801. The eNBdetermines whether ACK or NACK for each of the TBs has been transmitted,in step 803. If it is determined that the (NACK, ACK) signal has beentransmitted (i.e., a request for retransmission of TB1 has beentransmitted), the eNB receives the corresponding TB using the scramblingsequence of q=0 applied to Equation (2) and the UL RS for the firstlayer or the first and second layers, in step 811. The eNB transmits theACK/NACK for the retransmitted TB1 on the PHICH associated with I_(PRB)_(—) _(RA)=I_(PRB) _(—) _(RA) ^(lowest) ^(index) applied to Equation(5), in step 813. If it is determined that the (ACK, NACK) signal hasbeen transmitted (i.e., a request for retransmission of TB2 has beentransmitted), the eNB receives the corresponding TB using the scramblingsequence of q=1 applied to Equation (2) and the UL RS for the secondlayer UL RS, the second and third layers UL RS, or the third and fourthlayers UL RS, in step 821. The eNB transmits the ACK/NACK for theretransmitted TB2 on the PHICH associated with I_(PRB) _(—)_(RA)=I_(PRB) _(—) _(RA) ^(lowest) ^(—) ^(index)+1 applied to Equation(5), in step 823.

The UE and the eNB of the LTE system supporting UL MIMO, according toembodiments of the present invention, determine property parameters forUL retransmission independently. As a consequence, it is possible toperform the UL HARQ with no signal exchange for the property parameters.Thus, the UL HARQ between the UE and the eNB can be implemented onlywith the PHICH, resulting in improved efficiency of UL HARQ in the LTEsystem.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art that various changes in form an detail may be made thereinwithout departing from the spirit and scope, of the invention as definedby the appended claims.

1. A transmission method of a terminal supporting Uplink Multiple InputMultiple Output (UL MIMO), the method comprising the steps of:transmitting two transport blocks according to a predetermined number oflayers; and setting a precoding index for a lost transport block to apredetermined value, when one of the two transport blocks is lost. 2.The transmission method of claim 1, wherein setting the precoding indexcomprises maintaining the number of layers.
 3. The transmission methodof claim 1, further comprising: when both of the two transport blocksare lost, maintaining precoding indices used for transmission of the twotransport blocks; and retransmitting the two transport blocks using theprecoding indices.
 4. The transmission method of claim 1, wherein thepredetermined value is
 0. 5. A reception method of a base stationsupporting Uplink Multiple Input Multiple Output (UL MIMO), the methodcomprising the steps of: scheduling reception of two transport blocksaccording to a predetermined number of layers; transmitting a negativeacknowledgement for a lost transport block, when one of the twotransport blocks is lost; and setting a precoding index for receiving aretransmission of the lost transport block to a predetermined value. 6.The reception method of claim 5, wherein setting the precoding indexcomprises maintaining the number of layers.
 7. The reception method ofclaim 5, further comprising: when both of the two transport blocks arelost, maintaining precoding indices used for receiving the two transportblocks; and receiving the retransmission of the two transport blocksusing the precoding indices.
 8. A transmitter of a terminal supportingUplink Multiple Input Multiple Output (UL MIMO), comprising: a RadioFrequency (RF) processor that transmits two transport blocks to a basestation according to a predetermined number of layers; and a controllerthat sets a precoding index for a lost transport block to apredetermined value, when one of the two transport blocks is lost. 9.The transmitter of claim 8, wherein the controller maintains the numberof layers for retransmission of the lost transport block.
 10. Thetransmitter of claim 8, wherein the controller maintains precodingindices used for transmission of the two transport blocks andretransmits the two transport blocks using the precoding indices, whenboth of the two transport blocks are lost.
 11. The transmitter of claim8, wherein the predetermined value is
 0. 12. A receiver of a basestation supporting Uplink Multiple Input Multiple Output (UL MIMO),comprising: a controller that performs scheduling for reception of twotransport blocks according to a predetermined number of layers; and aRadio Frequency (RF) processor that transmits a negative acknowledgementfor a lost transport block, when one of the two transport blocks islost; wherein the controller sets a precoding index for reception of aretransmission of the lost transport block to a predetermined value. 13.The receiver of claim 12, wherein the controller maintains the number oflayers for reception of the retransmission of the lost transport block.14. The receiver of claim 12, wherein the controller maintains precodingindices used for receiving the tow transport blocks and receives theretransmission of the two transport blocks using the precoding indices,when both of the two transport blocks are lost.